Various systems are known for heat-sensitive recording. For example, heat-sensitive recording materials using an electron donating dye precursor and an electron accepting compound are disclosed in Japanese Patent Publication Nos. 14039/70 and 4160/68. Also, heat-sensitive recording materials using a diazo compound are disclosed in Japanese Patent Application (OPI) No. 190886/84 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application").
Recently, these heat-sensitive recording systems have been employed in various fields, such as facsimiles, printers, labellers, etc., and the need thereof have been rapidly increased. With such requirements, characteristics not previously required are now important factors. One of these characteristics is the reproducibility of print dots. In general, printout on a heat-sensitive recording paper is obtained by heating the heat-sensitive paper with a fine heating element of about 100 .mu.m.times.200 .mu.m in point area usually called a "thermal head" and it has been found to be important for obtaining a printout of high quality to reproduce faithfully the form of the fine heating element as a colored image or spot. This is called "print dot reproducibility".
Also, to fulfill the aforesaid requirement, incorporation of a heat-fusible material in a subbing layer of a heat-sensitive recording material has been proposed (Japanese Patent Application (OPI) No. 184691/84) but satisfactory print dot reproducibility has not yet been obtained.